The moon and Easter Sunday

By | April 24, 2011

It’s complicated, though. And it means Easter can come as early as March 22 — which it hasn’t since 1818 — or as late as April 25 — which it won’t again until 2038.

Moon confusion

Here’s the simplified formula: Easter falls on the first Sunday following the first full moon after the spring equinox. This year, the equinox fell on March 20, one day after the full moon. The next full moon wasn’t until April 18, so Easter is almost a week later, on April 24.

Confused? Well, there was once so much confusion that things came close to causing a schism.

Easter is the most important church feast, marking the Lord’s resurrection. In the earliest days, every Sunday was celebrated as if it were Easter. Christ’s followers gathered to commemorate his Passion, death and resurrection. To this day, every Sunday remains a celebration of Easter — even during Lent.

However, as time went on, Christians began to mark a special annual celebration of the resurrection, first called the “Pascha,” after the Jewish word for “Passover” (Pesach). Not everyone could agree on the date, however.

Some wanted it celebrated on the Jewish Passover, which can fall on any day of the week. Others wanted it to be on Sunday, since that was the day of the Lord’s resurrection.

Passover falls on the 14th day of Nissan, the first month of the Jewish calendar. (This year, Passover began after sunset April 19.) Christians who adhered to celebrating Easter on that day — no matter which day of the week — were known as “Quartodecimans” (based on the Latin word for 14). They were led by Polycarp of Smryna who claimed to be following the tradition of St. John the Evangelist. (Polycarp was a disciple of John.)

However, most Christians, following what was believed to be the tradition of the other apostles, chose Sunday for the Paschal feast. Things were not completely settled until the fourth century.

The Controversy

The “Easter controversy,” as it became known, got heated over which Sunday. By the second century, churches in Antioch and Syria based their Paschal feast on the Jewish calendar. Alexandria, and most of the churches of the Western Roman Empire, chose their Easter date independent of the Jewish calendar and tied it, in some way, to the spring equinox.

To show how heated the debate got, Pope Victor I, in 190, decreed that Easter would be on the Sunday following the 14th day of the full moon after the spring equinox. And, to avert a schism, he threatened to excommunicate anyone who didn’t agree.

Easter’s date (more correctly, its full moon) became tied to various calendars — solar, lunar, even Babylonian — and confusion continued.

Sunday rule

The Council of Nicea in 325 took on the challenge, but really only decided that Easter must be on a Sunday and must be tied the full moon. Generally, the Easter date followed the pattern set by the Alexandrian church, since Alexandria was the ancient world’s center of learning. Their date for Easter was on the Sunday two weeks after the Paschal moon, which brought it fairly close to the Passover date.

The 11th century break between the Eastern and Western churches again muddied the waters. The Western church began relying on astronomical full moons, while the Eastern church continued to follow the liturgical Paschal moon, which is not always the same as the spring equinox’s full moon.

Finally, around the Middle Ages, the formula in the West had settled into the one we are familiar with today: Easter falling on the Sunday after the first full moon following the spring equinox.

Faulty Calendar

The last major problem arose in the 16th century and you can still see it when you look at a calendar for next year: The Eastern Orthodox churches often celebrate Easter later than Latin-rite churches. Occasionally, we mark the feast on the same day, as we do this year and did last year. Next year, 2012, the Western church will celebrate Easter April 8; the Eastern churches will celebrate a week later.

This is because the Eastern churches use the Julian calendar to calculate Easter, while we in the West use the Gregorian calendar.

In 46 B.C., Julius Caesar devised the calendar bearing his name, but it was flawed. Julius’ calendar was 365 1/4 days long, about 11 minutes longer than a true solar year. Eleven minutes doesn’t seem like much but, by the 16th century, it had added up. So the Julian calendar’s spring equinox fell 10 days earlier than it astronomically took place. So Pope Gregory XIII (d. 1585) ordered a more accurate calendar and, to clear up errors, eliminated 10 days during October in 1582. The Gregorian calendar has 365 days, adding an extra day every fourth year.

The date of Easter still seems confusing. Yet the most important thing to remember is not the date, but what we have celebrated from the first days of the church: that the eternal God entered into human time through the incarnation so that, through the paschal mystery of Jesus Christ, God could draw all of us into eternity with him.

Sources: University of Utrecht at; “The Catholic Encyclopedia”; “Modern Catholic Dictionary”; “The HarperCollins Encyclopedia of Catholicism”; “Why Do Catholics Do That?”;” The Maryknoll Catholic Dictionary”; and “The Question Box”

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